The deal for this last condo, which measures 5,000 square feet, is expected to close Thursday. The price is $2.25 million, or $450 a square foot.

Inside Real Estate News calls the Four Seasons condos -- which take up the top 31 stories of the 45-story building at 14th and Arapahoe streets -- "the most expensive residential real estate project ever constructed in downtown..."

The Four Seasons opened in 2010, but the market made it tough to sell the condos. No unit sold that year or in 2011. A restructuring of the project's debt early this year led to lower prices for the condos and coincided with a renewed interest in luxury real estate.